1. Field
One embodiment of the invention relates to a circuit component with a projected portion, a printed circuit board and an electronic apparatus which are mounted with the circuit component.
2. Description of the Related Art
In a process for mounting circuit components on a printed wiring board, a solder paste is screen-printed on the wiring board, and the circuit components are set on the board and subjected to reflow processing. In mounting the circuit components on both obverse and reverse surfaces of the wiring board, some of the circuit components are first mounted on the obverse surface of the board in the aforesaid process. Then, the printed wiring board is turned over so that its reverse surface faces upward, the solder paste is printed on the reverse surface, and the other circuit components are set thereon and subjected again to the reflow processing.
In the reflow processing operation, the printed wiring board, carrying the circuit components thereon, is placed on a conveyor. Possibly, therefore, the printed wiring board may be vibrated to cause the circuit components to be dislocated. Further, the circuit components may be dislocated under the influence of a wind in a reflow oven or by the condensation force of the solder paste.
A circuit component that can be positioned with high accuracy is described in Jpn. Pat. Appln. KOKAI Publication No. 2002-184909. This circuit component is provided with a projected portion on the lower surface of a resin mold portion. On the other hand, a printed wiring board on which the circuit component is to be mounted is provided with a through hole corresponding to the projected portion. The circuit component is set on the wiring board in a manner such that its projected portion is inserted into the through hole. Thus, the circuit component can be securely tacked to the wiring board and positioned with high accuracy. In some cases, moreover, the projected portion may be provided on the circuit component in order to improve the mounting efficiency for the component on the wiring board.
Modern printed wiring boards that are mounted in electronic apparatuses, such as portable computers, are becoming thinner and thinner. If a printed wiring board is thin, the projected portion of the circuit component sometimes may penetrate the through hole of the board so that its distal end projects from the reverse surface of the board.
In mounting some circuit components on the reverse surface of the printed wiring board constructed in this manner, the solder paste is bound to be screen-printed on the reverse surface. Thus, if a metal mask for use as a screen plate is placed on the reverse surface of the wiring board, the distal end of the projected portion which projects from the reverse surface comes into contact with the mask. Inevitably, therefore, a gap is formed between the metal mask and the wiring board. If the solder paste is screen-printed with the gap left, the printing accuracy is unavoidably lowered. This adversely affects the reliability of the printed wiring board.
In the case of the thin printed wiring board, therefore, it is difficult to mount the circuit component including the projected portion by reflow processing. Accordingly, some circuit components with the projected portion are usually manually mounted one by one after other components are mounted on the obverse and reverse surfaces. This method, however, requires some improvement in view of manufacturability.